Читать книгу The life of Pasteur - René Vallery-Radot - Страница 13

Table of Contents

On January 30, 1860, the Académie des Sciences conferred on Pasteur the Prize for Experimental Physiology. Claude Bernard, who drew up the report, recalled how much Pasteur’s experiments in alcoholic fermentation, lactic fermentation, the fermentation of tartaric acid, had been appreciated by the Académie. He dwelt upon the great physiological interest of the results obtained. “It is,” he concluded, “by reason of that physiological tendency in Pasteur’s researches, that the Commission has unanimously selected him for the 1859 Prize for Experimental Physiology.”

That same January, Pasteur wrote to Chappuis: “I am pursuing as best I can these studies on fermentation which are of great interest, connected as they are with the impenetrable mystery of Life and Death. I am hoping to mark a decisive step very soon by solving, without the least confusion, the celebrated question of spontaneous generation. Already I could speak, but I want to push my experiments yet further. There is so much obscurity, together with so much passion, on both sides, that I shall require the accuracy of an arithmetical problem to convince my opponents by my conclusions. I intend to attain even that.”

This progress was depicted to his father in the following letter, dated February 7, 1860—

“I think I told you that I should read a second and last lecture on my old researches on Friday, at the Chemical Society, before several members of the Institute—amongst others, Messrs. Dumas and Claude Bernard. That lecture has had the same success as the first. M. Biot heard about it the next day through some distinguished persons who were in the audience, and sent for me in order to kindly express his great satisfaction.

“After I had finished, M. Dumas, who occupied the chair, rose and addressed me in these words. After praising the zeal I had brought to this novel kind of teaching at the Society’s request, and the so great penetration I had given proof of, in the course of the work I had just expounded, he added, ‘The Académie, sir, rewarded you a few days ago for other profound researches; your audience of this evening will applaud you as one of the most distinguished professors we possess.’

“All I have underlined was said in those very words by M. Dumas, and was followed by great applause.

“All the students of the scientific section of the Ecole Normale were present; they felt deeply moved and several of them have expressed their emotion to me.

“As for myself, I saw the realization of what I had foreseen. You know how I have always told you confidentially that time would see the growth of my researches on the molecular dissymmetry of natural organic products. Founded as they were on varied notions borrowed from divers branches of science—crystallography, physics, and chemistry—those studies could not be followed by most scientists so as to be fully understood. On this occasion I presented them in the aggregate with some clearness and power and every one was struck by their importance.

“It is not by their form that these two lectures have delighted my hearers, it is by their contents; it is the future reserved to those great results, so unexpected, and opening such entirely new vistas to physiology. I have dared to say so, for at these heights all sense of personality disappears, and there only remains that sense of dignity which is ever inspired by true love of science.

“God grant that by my persevering labours I may bring a little stone to the frail and ill-assured edifice of our knowledge of those deep mysteries of Life and Death where all our intellects have so lamentably failed.

“P.S.—Yesterday I presented to the Academy my researches on spontaneous generation; they seemed to produce a great sensation. More later.”

When Biot heard that Pasteur wished to tackle this study of spontaneous generation, he interposed, as he had done seven years before, to arrest him on the verge of his audacious experiments on the part played by dissymmetrical forces in the development of life. Vainly Pasteur, grieved at Biot’s disapprobation, explained that this question, in the course of such researches, had become an imperious necessity; Biot would not be convinced. But Pasteur, in spite of his quasi-filial attachment to Biot, could not stop where he was; he had to go through to the end.

“You will never find your way out,” cried Biot.

“I shall try,” said Pasteur modestly.

Angry and anxious, Biot wished Pasteur to promise that he would relinquish these apparently hopeless researches. J. B. Dumas, to whom Pasteur related the more than discouraging remonstrances of Biot, entrenched himself behind this cautious phrase—

“I would advise no one to dwell too long on such a subject.”

Senarmont alone, full of confidence in the ingenious curiosity of the man who could read nature by dint of patience, said that Pasteur should be allowed his own way.

It is regrettable that Biot—whose passion for reading was so indefatigable that he complained of not finding enough books in the library at the Institute—should not have thought of writing the history of this question of spontaneous generation. He could have gone back to Aristotle, quoted Lucretius, Virgil, Ovid, Pliny. Philosophers, poets, naturalists, all believed in spontaneous generation. Time went on, and it was still believed in. In the sixteenth century, Van Helmont—who should not be judged by that one instance—gave a celebrated recipe to create mice: any one could work that prodigy by putting some dirty linen in a receptacle, together with a few grains of wheat or a piece of cheese. Some time later an Italian, Buonanni, announced a fact no less fantastic: certain timberwood, he said, after rotting in the sea, produced worms which engendered butterflies, and those butterflies became birds.

Another Italian, less credulous, a poet and a physician, Francesco Redi, belonging to a learned society calling itself The Academy of Experience, resolved to carefully study one of those supposed phenomena of spontaneous generation. In order to demonstrate that the worms found in rotten meat did not appear spontaneously, he placed a piece of gauze over the meat. Flies, attracted by the odour, deposited their eggs on the gauze. From those eggs were hatched the worms, which had until then been supposed to begin life spontaneously in the flesh itself. This simple experiment marked some progress. Later on another Italian, a medical professor of Padua, Vallisneri, recognized that the grub in a fruit is also hatched from an egg deposited by an insect before the development of the fruit.

The theory of spontaneous generation, still losing ground, appeared to be vanquished when the invention of the microscope at the end of the seventeenth century brought fresh arguments to its assistance. Whence came those thousands of creatures, only distinguishable on the slide of the microscope, those infinitely small beings which appeared in rain water as in any infusion of organic matter when exposed to the air? How could they be explained otherwise than through spontaneous generation, those bodies capable of producing 1,000,000 descendants in less than forty-eight hours.

The world of salons and of minor courts was pleased to have an opinion on this question. The Cardinal of Polignac, a diplomat and a man of letters, wrote in his leisure moments a long Latin poem entitled the Anti-Lucretius. After scouting Lucretius and other philosophers of the same school, the cardinal traced back to one Supreme Foresight the mechanism and organization of the entire world. By ingenious developments and circumlocutions, worthy of the Abbé Delille, the cardinal, while vaunting the wonders of the microscope, which he called “eye of our eye,” saw in it only another prodigy offered us by Almighty Wisdom. Of all those accumulated and verified arguments, this simple notion stood out: “The earth, which contains numberless germs, has not produced them. Everything in this world has its germ or seed.”

Diderot, who disseminated so many ideas (since borrowed by many people and used as if originated by them), wrote in some tumultuous pages on nature: “Does living matter combine with living matter? how? and with what result? And what about dead matter?”

About the middle of the eighteenth century the problem was again raised on scientific ground. Two priests, one an Englishman, Needham, and the other an Italian, Spallanzani, entered the lists. Needham, a great partisan of spontaneous generation, studied with Buffon some microscopic animalculæ. Buffon afterwards built up a whole system which became fashionable at that time. The force which Needham found in matter, a force which he called productive or vegetative, and which he regarded as charged with the formation of the organic world, Buffon explained by saying that there are certain primitive and incorruptible parts common to animals and to vegetables. These organic molecules cast themselves into the moulds or shapes which constituted different beings. When one of those moulds was destroyed by death, the organic molecules became free; ever active, they worked the putrefied matter, appropriating to themselves some raw particles and forming, said Buffon, “by their reunion, a multitude of little organized bodies, of which some, like earthworms, and fungi, seem to be fair-sized animals or vegetables, but of which others, in almost infinite numbers, can only be seen through the microscope.”

All those bodies, according to him, only existed through spontaneous generation. Spontaneous generation takes place continually and universally after death and sometimes during life. Such was in his view the origin of intestinal worms. And, carrying his investigations further, he added, “The eels in flour paste, those of vinegar, all those so-called microscopic animals, are but different shapes taken spontaneously, according to circumstances, by that ever active matter which only tends to organization.”

The Abbé Spallanzani, armed with a microscope, studied these infinitesimal beings. He tried to distinguish them and their mode of life. Needham had affirmed that by enclosing putrescible matter in vases and by placing those vases on warm ashes, he produced animalculæ. Spallanzani suspected: firstly that Needham had not exposed the vases to a sufficient degree of heat to kill the seeds which were inside; and secondly, that seeds could easily have entered those vases and given birth to animalculæ, for Needham had only closed his vases with cork stoppers, which are very porous.

“I repeated that experiment with more accuracy,” wrote Spallanzani. “I used hermetically sealed vases. I kept them for an hour in boiling water, and after having opened them and examined their contents within a reasonable time I found not the slightest trace of animalculæ, though I had examined with the microscope the infusions from nineteen different vases.”

Thus dropped to the ground, in Spallanzani’s eyes, Needham’s singular theory, this famous vegetative force, this occult virtue. Yet Needham did not own himself beaten. He retorted that Spallanzani had much weakened, perhaps destroyed, the vegetative force of the infused substances by leaving his vases in boiling water during an hour. He advised him to try with less heat.

The public took an interest in this quarrel. In an opuscule entitled Singularities of Nature (1769), Voltaire, a born journalist, laughed at Needham, whom he turned into an Irish Jesuit to amuse his readers. Joking on this race of so-called eels which began life in the gravy of boiled mutton, he said: “At once several philosophers exclaimed at the wonder and said, ‘There is no germ; all is made, all is regenerated by a vital force of nature.’ ‘Attraction,’ said one; ‘Organized matter,’ said another, ‘they are organic molecules which have found their casts.’ Clever physicists were taken in by a Jesuit.”

In those pages, lightly penned, nothing remained of what Voltaire called “the ridiculous mistake, the unfortunate experiments of Needham, so triumphantly refuted by M. Spallanzani and rejected by whoever has studied nature at all.” “It is now demonstrated to sight and to reason that there is no vegetable, no animal but has its own germ.” In his Philosophic Dictionary, at the word God, “It is very strange,” said Voltaire, “that men should deny a creator and yet attribute to themselves the power of creating eels!” The Abbé Needham, meeting with these religious arguments, rather unexpected from Voltaire, endeavoured to prove that the hypothesis of spontaneous generation was in perfect accordance with religious beliefs. But both on Needham’s side and on Spallanzani’s there was a complete lack of conclusive proofs.

Philosophic argumentation always returned to the fore. As recently as 1846 Ernest Bersot (a moralist who became later a director of the Ecole Normale) wrote in his book on Spiritualism: “The doctrine of spontaneous generation pleases simplicity-loving minds; it leads them far beyond their own expectations. But it is yet only a private opinion, and, were it recognized, its virtue would have to be limited and narrowed down to the production of a few inferior animals.”

That doctrine was about to be noisily re-introduced.

On December 20, 1858, a correspondent of the Institute, M. Pouchet, director of the Natural History Museum of Rouen, sent to the Académie des Sciences a Note on Vegetable and Animal Proto-organisms spontaneously Generated in Artificial Air and in Oxygen Gas. The note began thus: “At this time when, seconded by the progress of science, several naturalists are endeavouring to reduce the domain of spontaneous generation or even to deny its existence altogether, I have undertaken a series of researches with the object of elucidating this vexed question.” Pouchet, declaring that he had taken excessive precautions to preserve his experiments from any cause of error, proclaimed that he was prepared to demonstrate that “animals and plants could be generated in a medium absolutely free from atmospheric air, and in which, therefore, no germ of organic bodies could have been brought by air.”

On one copy of that communication, the opening of a four years’ scientific campaign, Pasteur had underlined the passages which he intended to submit to rigorous experimentation. The scientific world was discussing the matter; Pasteur set himself to work.

A new installation, albeit a summary one, allowed him to attempt some delicate experiments. At one of the extremities of the façade of the Ecole Normale, on the same line as the doorkeeper’s lodge, a pavilion had been built for the school architect and his clerk. Pasteur succeeded in obtaining possession of this small building, and transformed it into a laboratory. He built a drying stove under the staircase; though he could only reach the stove by crawling on his knees, yet this was better than his old attic. He also had a pleasant surprise—he was given a curator. He had deserved one sooner, for he had founded the institution of agrégés préparateurs. Remembering his own desire, on leaving the Ecole Normale, to have a year or two for independent study, he had wished to facilitate for others the obtaining of those few years of research and perhaps inspiration. Thanks to him, five places as laboratory curators were exclusively reserved to Ecole Normale students who had taken their degree (agrégés). The first curator who entered the new laboratory was Jules Raulin, a young man with a clear and sagacious mind, a calm and tenacious character, loving difficulties for the sake of overcoming them.

Pasteur began by the microscopic study of atmospheric air. “If germs exist in atmosphere,” he said, “could they not be arrested on their way?” It then occurred to him to draw—through an aspirator—a current of outside air through a tube containing a little plug of cotton wool. The current as it passed deposited on this sort of filter some of the solid corpuscles contained in the air; the cotton wool often became black with those various kinds of dust. Pasteur assured himself that amongst various detritus those dusts presented spores and germs. “There are therefore in the air some organized corpuscles. Are they germs capable of vegetable productions, or of infusions? That is the question to solve.” He undertook a series of experiments to demonstrate that the most putrescible liquid remained pure indefinitely if placed out of the reach of atmospheric dusts. But it was sufficient to place in a pure liquid a particle of the cotton-wool filter to obtain an immediate alteration.

A year before starting any discussion Pasteur wrote to Pouchet that the results which he had attained were “not founded on facts of a faultless exactitude. I think you are wrong, not in believing in spontaneous generation (for it is difficult in such a case not to have a preconceived idea), but in affirming the existence of spontaneous generation. In experimental science it is always a mistake not to doubt when facts do not compel affirmation.... In my opinion, the question is whole and untouched by decisive proofs. What is there in air which provokes organization? Are they germs? is it a solid? is it a gas? is it a fluid? is it a principle such as ozone? All this is unknown and invites experiment.”

After a year’s study, Pasteur reached this conclusion: “Gases, fluids, electricity, magnetism, ozone, things known or things occult, there is nothing in the air that is conditional to life, except the germs that it carries.”

Pouchet defended himself vigorously. To suppose that germs came from air seemed to him impossible. How many millions of loose eggs or spores would then be contained in a cubic millimetre of atmospheric air?

“What will be the outcome of this giant’s struggle?” grandiloquently wrote an editor of the Moniteur Scientifique (April, 1860). Pouchet answered this anonymous writer by advising him to accept the doctrine of spontaneous generation adopted of old by so many “men of genius.” Pouchet’s principal disciple was a lover of science and of letters, M. Nicolas Joly, an agrégé of natural science, doctor of medicine, and professor of physiology at Toulouse. He himself had a pupil, Charles Musset, who was preparing a thesis for his doctor’s degree under the title: New Experimental Researches on Heterogenia, or Spontaneous Generation. By the words heterogenia or spontaneous generation Joly and Musset agreed in affirming that “they did not mean a creation out of nothing, but the production of a new organized being, lacking parents, and of which the primordial elements are drawn from ambient organic matter.”

Thus supported, Pouchet multiplied objections to the views of Pasteur, who had to meet every argument. Pasteur intended to narrow more and more the sphere of discussion. It was an ingenious operation to take the dusts from a cotton-wool filter, to disseminate them in a liquid, and thus to determine the alteration of that liquid; but the cotton wool itself was an organic substance and might be suspected. He therefore substituted for the cotton wool a plug of asbestos fibre, a mineral substance. He invented little glass flasks with a long curved neck; he filled them with an alterable liquid, which he deprived of germs by ebullition; the flask was in communication with the outer air through its curved tube, but the atmospheric germs were deposited in the curve of the neck without reaching the liquid; in order that alteration should take place, the vessel had to be inclined until the point where the liquid reached the dusts in the neck.

But Pouchet said, “How could germs contained in the air be numerous enough to develop in every organic infusion? Such a crowd of them would produce a thick mist as dense as iron.” Of all the difficulties this last seemed to Pasteur the hardest to solve. Could it not be that the dissemination of germs was more or less thick according to places? “Then,” cried the heterogenists, “there would be sterile zones and fecund zones, a most convenient hypothesis, indeed!” Pasteur let them laugh whilst he was preparing a series of flasks reserved for divers experiments. If spontaneous generation existed, it should invariably occur in vessels filled with the same alterable liquid. “Yet it is ever possible,” affirmed Pasteur, “to take up in certain places a notable though limited volume of ordinary air, having been submitted to no physical or chemical change, and still absolutely incapable of producing any alteration in an eminently putrescible liquor.” He was ready to prove that nothing was easier than to increase or to reduce the number either of the vessels where productions should appear or of the vessels where those productions should be lacking. After introducing into a series of flasks of a capacity of 250 cubic centimetres a very easily corrupted liquid, such as yeast water, he submitted each flask to ebullition. The neck of those vessels was ended off in a vertical point. Whilst the liquid was still boiling, he closed, with an enameller’s lamp, the pointed opening through which the steam had rushed out, taking with it all the air contained in the vessel. Those flasks were indeed calculated to satisfy both partisans or adversaries of spontaneous generation. If the extremity of the neck of one of these vessels was suddenly broken, all the ambient air rushed into the flask, bringing in all the suspended dusts; the bulb was closed again at once with the assistance of a jet of flame. Pasteur could then carry it away and place it in a temperature of 25-30° C., quite suitable for the development of germs and mucors.

In those series of tests some flasks showed some alteration, others remained pure, according to the place where the air had been admitted. During the beginning of the year 1860 Pasteur broke his bulb points and enclosed ordinary air in many different places, including the cellars of the Observatory of Paris. There, in that zone of an invariable temperature, the absolutely calm air could not be compared to the air he gathered in the yard of the same building. The results were also very different: out of ten vessels opened in the cellar, closed again and placed in the stove, only one showed any alteration; whilst eleven others, opened in the yard, all yielded organized bodies.

In a letter to his father (June, 1860), Pasteur wrote: “I have been prevented from writing by my experiments, which continue to be very curious. But it is such a wide subject that I have almost too many ideas of experiments. I am still being contradicted by two naturalists, M. Pouchet of Rouen and M. Joly of Toulouse. But I do not waste my time in answering them; they may say what they like, truth is on my side. They do not know how to experiment; it is not an easy art; it demands, besides certain natural qualities, a long practice which naturalists have not generally acquired nowadays.”

When the long vacation approached, Pasteur, who intended to go on a voyage of experiments, laid in a store of glass flasks. He wrote to Chappuis, on August 10, 1860: “I fear from your letter that you will not go to the Alps this year.... Besides the pleasure of having you for a guide, I had hoped to utilize your love of science by offering you the modest part of curator. It is by some study of air on heights afar from habitations and vegetation that I want to conclude my work on so-called spontaneous generation. The real interest of that work for me lies in the connection of this subject with that of ferments which I shall take up again November.”

Pasteur started for Arbois, taking with him seventy-three flasks; he opened twenty of them not very far from his father’s tannery, on the road to Dôle, along an old road, now a path which leads to the mount of the Bergère. The vine labourers who passed him wondered what this holiday tourist could be doing with all those little phials; no one suspected that he was penetrating one of nature’s greatest secrets. “What would you have?” merrily said his old friend, Jules Vercel; “it amuses him!” Of those twenty vessels, opened some distance away from any dwelling, eight yielded organized bodies.

Pasteur went on to Salins and climbed Mount Poupet, 850 metres above the sea-level. Out of twenty vessels opened, only five were altered. Pasteur would have liked to charter a balloon in order to prove that the higher you go the fewer germs you find, and that certain zones absolutely pure contain none at all. It was easier to go into the Alps.

He arrived at Chamonix on September 20, and engaged a guide to make the ascent of the Montanvert. The very next morning this novel sort of expedition started. A mule carried the case of thirty-three vessels, followed very closely by Pasteur, who watched over the precious burden and walked alongside of precipices supporting the case with one hand so that it should not be shaken.

When the first experiments were started an incident occurred. Pasteur has himself related this fact in his report to the Académie. “In order to close again the point of the flasks after taking in the air, I had taken with me an eolipyle spirit-lamp. The dazzling whiteness of the ice in the sunlight was such that it was impossible to distinguish the jet of burning alcohol, and as moreover that was slightly moved by the wind, it never remained on the broken glass long enough to hermetically seal my vessel. All the means I might have employed to make the flame visible and consequently directable would inevitably have given rise to causes of error by spreading strange dusts into the air. I was therefore obliged to bring back to the little inn of Montanvert, unsealed, the flasks which I had opened on the glacier.”

The inn was a sort of hut, letting in wind and rain. The thirteen open vessels were exposed to all the dusts in the room where Pasteur slept; nearly all of them presented alterations.